1. Technical Field
The present invention relates generally to prosthetic devices used in elbow arthroplasty and more particularly to a modular elbow prosthesis.
2. Background Art
Linked or constrained elbow prosthesis are known which comprise simple hinge arrangements, one component of which is attached to the end of the humerus and the other component of which is attached to the end of the ulna. The humeral component includes a shaft that is cemented into a prepared cavity in the end of the humerus, and the ulnar component includes a shaft, that is cemented to end of the ulna. The components of the prosthesis are connected together by means of a hinge pin so that the prosthesis allows a single degree of freedom of movement of the ulna relative to the humerus.
One example of a link elbow prostheses is disclosed in U.S. Pat. No. 6,027,534 to Wack et al. In several respects, the linked embodiment of the '534 patent is typical of the designs for linked elbow prostheses in that it includes a humeral stem that terminates at a yoke at its distal end, a bearing component, retaining pin and an ulna stem. The bearing component includes an oversized hole that is aligned with the longitudinal axis of the bearing and adapted to accept the retaining pin in a slip-fit condition. The distal end of the bearing component is coupled to the ulna stem. Despite the relatively widespread use of the designs of the type, several drawbacks have been noted.
One significant drawback concerns the assembly of the elbow prosthesis after the surgeon has cemented the humeral and ulna stems to their respective bones. In using such conventionally configured linked elbow prosthesis devices, it is frequently necessary for the surgeon to drill a fairly large hole through the humerus so that the retaining pin may be inserted to the yoke of the humeral stem and the humeral bearing component. As a high degree of accuracy is typically required to ensure proper alignment between the hole in the humerus and the hole in the yoke of the humeral stem, a significant cost can be associated with this step in the installation of an elbow prosthesis due to the cost of the tooling used and the amount of amount of time required to complete this step. The other method for attaching the prosthetic device includes inserting the device in its linked condition or placing the remaining piece into the yoke prior to fully seating the humeral component into the bone. This later method is typically somewhat difficult, given the limited amount of joint space that is available and the time constraints associated with a use of a PMMA bone cement.
Unlinked, or unconstrained, elbow prostheses are known which are similar to linked elbow prostheses but do not have a specific component which mechanically couples the humeral and ulnar stems together. Rather, prosthetic device is held together by the patient's natural soft tissues. One example of an unlinked elbow prostheses is also disclosed in U.S. Pat. No. 6,027,534 to Wack et al. In several respects, the unlinked embodiment of the '534 patent is similar to the linked embodiment discussed above in that it includes a humeral stem that terminates at a yoke at its distal end, a humeral bearing component, a retaining pin, an ulnar bearing component and a ulnar stem. The outer surface of the humeral bearing is contoured to match the contour of the ulnar bearing component. Despite the relativity widespread use of designs of this type, several drawbacks have been noted.
For instance, a retaining pin that is transverse to the longitudinal axis of the patient is employed, thereby making its removal difficult if a bearing need to be replaced.